<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>遮盖</title>
    <style>
        .bg{
            height: 300px;
            width: 300px;
            background: red;
            position: relative;
            overflow: hidden;
        }
        .bg:hover{
            transform: rotate(0deg);
        }
        .cover{
            height: 300px;
            width: 300px;
            position: absolute;
            top: 0;
            left: 0;
            background:rgba(77, 76, 76, 0.616);
            z-index: 100;
            transform-origin: right bottom;
            transform: rotate(90deg);
            transition: all 1s;
        }
        .bg:hover .cover{
            transform: rotate(0deg);
        }
    </style>
</head>
<body>
    <div class="bg">
        <div class="cover"></div>
    </div>
    
</body>
</html>